In VSS2008 we presented the intermittent feedback model of goal-directed forearm movement. In the model a goal-directed movement consists of two submovements, with the trajectory of each submovement being individually optimized. Simulations using the model showed that the optimal transition between two submovements occurs at an early stage of the movement, and produces a sharp increase in the acceleration profile in agreement with the preliminary psychophysical data.

In the present study, we directly measured the acceleration profiles of goal-directed movement using accelerometer to avoid the large noise caused by successive differentiations. The new data allows us to examine the patterns of individual trials in addition to verifying the previous findings. Analysis of individual trials show that the time of peak acceleration is relatively constant across the trials, and the amplitude of this peak systematically affects the shape of the acceleration profile during the later stages of the movement. These profiles are very similar to those produced by the model. All these results confirm the model's prediction that humans apply early correction just after the initiation of the goal-directed movement. Finally, we tested our model in various distance and accuracy conditions. We found that the simulated movement durations across conditions are consistent with Fitts' law.